Integrated circuit (“IC”) packages are ubiquitous in modern electronic devices. A typical integrated circuit package includes an IC die (“chip”), a lead frame and a layer of protective encapsulant. Lead frames are formed by cutting a pattern in a thin sheet of conductive material such as copper. Lead frames typically come in strip form with many identical lead frame patterns provided in a grid array on the strip.
An IC die (sometimes referred to herein simply as “die”) is a small block of semiconductor material such as silicon in which an electrical circuit that performs a predetermined function is provided. Dies often have contact pads on a top surface that allow the die circuit to be connected to external circuits.
The usual method of forming IC packages includes mounting a number of identical dies on identical lead frame portions of a lead frame strip. After the dies are mounted on the lead frame strip, the dies are electrically connected to the corresponding lead frames. In a typical process, contact pads on the dies are electrically connected to predetermined regions on the corresponding lead frames by small thin wires by a process called wire bonding. In some cases it may be desirable to incorporate additional functionality into each die by attaching a discrete circuit device to the die. The discrete circuit device is often a passive circuit element, e.g. a capacitor, inductor or resistor. Or the discrete device may be a more complex circuit device, such as a sensor, a microelectromechanical system (MEMS), an oscillator or a smaller IC. The discrete circuit device is typically provided in a small box shaped configuration with a pair of external contacts that are attached to two contact pads on a corresponding die or other electrical substrate.
After wire bonding and attachment of the discrete circuit device(s) are completed the lead frame strips are moved to a mold station, such as a transfer mold station, where a mold compound is applied that covers the dies, wire bonds, discrete circuit device(s) and most of the surface of each of the lead frames. Small end portions of each lead frame are not coated with mold compound to provide exposed contacts for the subsequently formed IC packages. The applied mold compound is heated under pressure until it cures to a solid state. The cured mold compound or “encapsulant” protects the encapsulated portions of each lead frame and the associated die, wire bond connections and discrete device.
After curing of the mold compound, the lead frame strip is cut apart or “singulated” to separate the strip into individual IC packages. In one typical situation, each IC package includes an encapsulated die, wire bonds, discrete device, and an encapsulated lead frame with projecting electrical contacts.